1. Field of the Invention
The present invention relates to a rotary vane compressor for an air conditioning system used in a vehicle such as automobile, and more particularly, it relates to a variable displacement vane compressor in which a rotor having at least one vane is rotatably housed in a cylindrical housing, both ends of which are closed by a pair of side plates to define at least one pressure chamber between an outer surface of the rotor and an inner surface of the housing, so that the pressure chamber is expanded and compressed while communicating in turn with an inlet port and an outlet port, to draw in a refrigerant and to compress and discharge the refrigerant, and in which a displacement control plate for controlling a maximum displacement of the compressor is rotatably disposed between the rotor and one of the side plates.
2. Description of the Related Arts
Conventionally, a variable displacement vane compressor of the above type is driven by an engine of an automobile, so that the cabin temperature of the automobile is adjusted to a temperature at which the driver and passengers feel comfortable under ambient conditions. When a cooling load of the air conditioning system becomes high, the compressor must operate at the maximum cooling capacity thereof, and when the cooling load becomes lower, the compressor preferably operates at a lower cooling capacity. Further, when the cabin temperature once reaches a desired temperature, the compressor preferably operates at the minimum cooling capacity at which the desired temperature can be maintained.
U.S. patent application Ser. No. 902,311 (corresponding to Japanese Unexamined Patent Publication No. 62-55487) filed by the same applicant discloses an improvement of a variable displacement vane compressor of the above type, wherein a compression mode carried out by the vane is adjustable in response to a pressure change of the refrigerant within a suction chamber of the compressor, which is connected to an evaporator of the air conditioning system, whereby an amount of compressed refrigerant discharged from the compressor into the air conditioning system can be varied in response to a cooling load of the air conditioning system. Namely, this compressor comprises an annular plate member rotatably disposed between one of the end wall members of the cylinder assembly and the cylindrical body thereof. The annular plate member has an arcuate slot extending in the rotational direction of the vane and opening to the crescent chamber. The vane passes through the crescent chamber in such a manner that the vane divides the crescent chamber into a front and a rear section, with a volume of the front section being gradually decreased while a volume of the rear section is gradually increased. While the vane advances along the arcuate slot of the annular plate member, a part of the refrigerant received in the front section is allowed to escape into the rear section through the arcuate slot, and thus the compression mode starts just after the vane has passed through the arcuate slot of the annular plate member. With this arrangement, it is possible to adjust the compression mode by moving the annular plate member in the rotational direction of the vane in response to a pressure change of the refrigerant within the suction room of the compressor.
This movement of the annular plate member is caused by a spool member slidably accommodated in a cylindrical bore. The spool member divides the bore into two compartments, one of which (a first compartment) is always communicated with a discharging chamber into which the compressed refrigerant is discharged from the crescent chamber, and the other (a second compartment) receives a compression spring to bias the spool toward the first compartment and is communicated with a reservoir for lubricant oil pressurized to a pressure corresponding to that of the discharged refrigerant. The introduction of the oil into the second compartment is controlled by a check valve arranged midway in an oil path extending from the oil reservoir to the second compartment. The check valve operates in response to a change of the interior pressure of the suction chamber in such a manner that, when this pressure is lowered, the check valve allows a larger amount of the oil to flow into the second compartment and, conversely, when the pressure becomes higher, narrows the passage to limit the amount of the oil. The spool is displaced in the bore until a dynamic balance of the interior pressure between both compartments is attained, whereby the annular plate member is rotatably displaced in response to the movement of the spool. To obtain a proper displacement of the annular plate member, the interior pressure of the first compartment must be correctly maintained at a level corresponding to the interior pressure of the discharging chamber. The refrigerant (gas) filled in the second compartment, however, tends to leak therefrom to a lower pressure region in the compressor, mainly through an evitable micro-gap between a surface of the annular plate member and the associated surface of the end wall member in contact therewith. Thus, the dynamic balance of pressure between both compartments is only attained when the spool is displaced from the proper position towards the first compartment side.